The present invention relates to color-picture tubes with a screen coated with groups of phosphor stripes, areas of which are caused to glow by electrons incident on them, which electrons are deflected by a deflection system.
Various technical solutions have been provided for reproducing colors with color-picture tubes. Most of them are based on the assumption that three independent variables are required for unambiguously defining a color. Each color is given by chromaticity and luminance. To define chromaticity, two independent variables are required. Therefore, chromaticity can be easily presented in two-dimensional representations, such as the color circle or the chromaticity diagram. In most types of color-picture tubes, the three variables are realized by choosing three primary colors, usually red, green and blue, selecting corresponding phosphors, and exciting each of these phosphors with electron beams and with different beam currents. In that case, therefore, the three independent variables are the electron beam currents, which can be varied independently of each other.
The various color-picture tube systems differ in the method by which the electron beams are caused to hit the phosphors they are meant to strike. In the system which is in most widespread use, groups of vertical primary color-phosphor stripes are deposited on a screen, and an electron beam sweeps horizontally across these stripes. Before striking the phosphor stripes, the beam passes through a so-called color selection electrode. This method leads to excellent color reproductions but is very expensive. DE-OS 25 23 524 discloses a color-picture tube in which no color selection electrode is required. Groups of horizontal phosphor stripes are swept horizontally by three electron beams whose currents are adjustable independently of each other. This solution represents a considerable simplification over color-picture tubes having color selection electrodes. A major problem is, however, that each of the three electron beams must at any time be precisely adjusted to prevent an electron beam assigned to, e.g., the primary color red from also exciting phosphor stripes of the color green or blue.